Selective Area Processing is a technique where material, typically metal, is removed from a workpiece. The removal of this material is traditionally accomplished using a sputtering process.
In certain systems, a sputtering material, such as argon, is extracted from a plasma chamber through an extraction aperture toward the workpiece. The extraction optics of the plasma chamber may include an extraction plate, which is located in close proximity, such as between 7 and 20 mm, from the workpiece. The sputtering material impacts the workpiece, causing a metal on the workpiece to be removed.
However, there are several issues associated with selective area processing, such as particle generation and beam current drift. As the argon strikes the workpiece, metal atoms, such as tungsten, are removed. These metal atoms obey a Lambertian distribution and as a result, most of the removed metal atoms redeposit on the extraction plate or enter the plasma chamber through the extraction aperture. The material that arrives at the extraction plate grows in a thin film, and when its thickness reaches a certain value, the film exfoliates, generating particles, which may contaminate the workpiece. The material that enters the plasma chamber may deposit on the dielectric window, which is disposed between the plasma chamber and the RF antenna. Since these metal atoms are conductive, they reduce the RF power coupling efficiency, thus reducing plasma density and extraction ion beam current during operation.
Currently, these issues are resolved by a maintenance process, where the plasma chamber is shut down for an extended period of time so that the surfaces may all be cleaned. After cleaning is complete, vacuum is re-established and the plasma chamber is ready for use. However, this down time hurts operational efficiency and reduces throughput.
Thus, it would be beneficial if there was an apparatus which could control allow fast, automated in situ cleaning of these metal deposits. Further, it would beneficial if the apparatus could clean the deposits on the extraction plate and within the plasma chamber at different rates, if desired. Such an apparatus may be beneficial in certain applications, such as selective area processing.